First responders need a cost-effective method to detect fentanyl, a potent synthetic opioid, in the field. A new electrochemical sensor takes as little as 1 min to identify the drug (Anal. Chem. 2019, DOI: 10.1021/acs.analchem.9b00176). Joseph Wang of the University of California San Diego screen printed carbon and silver-chloride electrodes onto poly(ethylene terephthalate). The team treated the carbon electrodes with an ionic liquid to stabilize them and to help fentanyl accumulate on the surface. These disposable strips are easy to produce and cost only a few cents apiece, Wang says. The researchers applied samples of fentanyl to the strips and inserted them into an electrochemical device that delivers alternating cycles of increasing and decreasing voltage to the test strip. Fentanyl undergoes oxidation and reduction at specific voltages, which changes how much current passes through the carbon electrode compared with the reference electrode, and generates a unique signature. This signature remained detectable in the presence of common cutting agents. Harvard University chemist George M. Whitesides says the method is promising but needs to be tested on complex street-drug samples.